1. Field of the Invention
The field of the present invention relates to an automatic sliding doors and control/security systems therefor, particularly well suited for use in walk-in freezer or refrigerator units.
2. Background
In the past, doors used on walk-in freezer and refrigerator units have often been swinging-type doors that need to be manually opened and closed. However, manual operation of freezer or refrigerator doors can be quite inconvenient, especially when there is a large amount of traffic passing into and out of the walk-in freezer or refrigerator unit, or when persons needing access to the walk-in freezer or refrigerator unit are laden with trays or other bulky items which need to be set aside to allow manual opening of the door, followed by the extra effort of re-lifting and balancing the trays or other bulky items.
Swinging-type doors can also be hazardous to persons in close proximity to the doors, when passers-through open the doors suddenly as they enter or exit the freezer or refrigerator unit. The swinging of the door can cause serious physical harm to persons, or knock trays of food or fragile items out of their hands.
Sliding doors have been designed for use in walk-in freezer or refrigerator units. Generally, such sliding doors have been motor-driven, but require manual activation, such as by pulling on a cord or pushing a button. Such manual operation of refrigerator or freezer sliding doors can be inconvenient to persons carrying items or pushing heavy carts. Further, particularly since refrigerator or freezer doors are often large, thick and heavy, the motors used to open and close such sliding doors are generally gear-driven or hydraulic in nature, and are prone to wear and tear.
Automatic swinging doors and sliding doors have been used in supermarkets and similar environments. Sensors are typically used in automatic door systems to assist the control electronics in determining when to start or stop opening the doors. Typically, a small mechanical switch known as a microswitch is employed to indicate the stopping point for the doors. The motor drive mechanism drives the doors past the microswitch which, when the door passes, physically switches, causing an output electrical signal indicating that the door is passing. When the controller receives the microswitch signal, it commands the motor drive to stop the motion of the door. Microswitches are generally mechanical in nature, and are required to be physically moved a slight distance (e.g., by the passing of the door) in order to produce an output signal. Being mechanical in nature, microswitches are prone to wear and tear, and deterioration over time.
Other means that have been used to control the opening and closing of automatic doors are proximity detectors. Proximity detectors are generally capacitive or inductive in nature, operating on the presence or absence of a magnetic field.
Designing doors for walk-in freezer and refrigerator units involve special challenges due to the effects of the cold environment on equipment and the door structure and components. Thus, sliding doors used in supermarket environments generally are not suitable for use in walk-in freezer or refrigerator units. Further, a wide variety of safety concerns exist in the walk-in freezer or refrigerator environment which are not present, or are less present, in the supermarket environment. For example, due care must be taken to avoid the possibility of persons being trapped inside a walk-in freezer or refrigerator unit due to failure or locking of the door mechanism.
There is a need for an automated door that is particularly well adapted for use in walk-in freezer or refrigerator units. There is further a need for such an automated door system that provides a high degree of safety for users, and prevents to a maximum degree obtainable the possibility that persons may become inadvertently trapped inside a walk-in freezer or refrigerator unit.